It is well known that a body moving through a fluid experiences skin friction, or drag forces, which arise within the so-called boundary layer, adjacent the outer surface of the body. Flow within this layer may be either laminar or turbulent, the skin friction resulting from the former being less than that from the latter. To increase the area of the body over which the flow is laminar, it is advantageous to remove some of the boundary layer from the surface by suction, that is by drawing some of the fluid into the body through the surface.
Several approaches have been taken to accomplish this goal. One suggestion has been to provide a continuous, porous surface over a large area of the body. Problems arise since, in general, the porous materials utilized are not able to adequately withstand the stresses applied. Also, with a large area of porous material exposed to the environment, flow impedence or clogging frequently result.
It has also been suggested that a plurality of spanwise slits over an open vacuum slot be provided. However, these have proved difficult and costly to produce due to manufacturing complexities including, for example, the close tolerances required. Since these slits have usually been cut on the complex contours of, for example, an airfoil, skilled craftsmen and special tools have been necessary. In an effort to avoid this problem, it has been further suggested that prefabricated strips, containing suction slits, be used. This approach again requires special tools to produce a carefully machined ledge in the suction slot to hold the prefabricated strip, since the surface containing the slot is frequently a complex contour. Even where the body contour is relatively simple, close machining tolerances have been necessary due to surface smoothness requirements after the strip is installed.
The industry has long sought an inexpensive method of providing boundary layer suction that does not require complex machining equipment.
Accordingly, it is an object of the present invention to overcome the disadvantages set forth above and to provide a simple and inexpensive method and apparatus for obtaining the desired surface smoothness in a body.
More particularly, it is an object of this invention to provide a simple and inexpensive method of installing a laminar flow control suction insert to a body.
It is a further object of this invention to provide a simple and inexpensive method of attaching insert strips to a body.
It is yet another object of this invention to provide a method of installing a laminar flow control suction slit system in the surface of an airfoil, which method requires neither close machining tolerances nor complex installation procedures.
It is a further object of this invention to provide a method of attaching inserts to airfoils, which method requires neither extremely skilled personnel nor complex and expensive tools.
It is another object of the invention to provide an insert strip, for use in a laminar flow control-type body, that may be easily and inexpensively removed and replaced when necessary.